Electrically insulated sealant and containment caps have been used to cover an end portion of a metallic bolt assembly which typically includes one or more washer(s), a nut and a threaded end portion of a bolt shaft which extends beyond the nut. The sealant caps electrically insulate the end portion of the metallic bolt assembly so as electrically isolate and contain the end portion from important vicinities surrounding the end portion of the metallic bolt assembly such as a fuel tank within an aircraft. Electrically isolating and containing the end portion of the metallic bolt assembly prevents unwanted sparks or electrical current transmissions entering such important vicinities upon an EME/lightning event.
The insulation and containment caps are made from sealant material such as for example a thermoset plastic. The caps are also filled with a liquid form of sealant material. Once the cap is filled with liquid sealant the cap is positioned over the end portion of the metallic bolt assembly enclosing the end portion of the metallic bolt assembly within the cap and a surface from which the end portion of the metallic bolt assembly extends. The liquid sealant that is expelled from the cap from placing the cap over the end portion of the metallic bolt assembly requires fairing. The cap also requires being held in place for a time period to maintain the cap's position so as to prevent occurrence of the cap experiencing slumping or lifting off of the surface and the end portion of the metallic bolt assembly during the curing of the sealant. The quality standards for fairing these caps are high which makes installation time consuming and places the installation at high risk of failing quality checks resulting in increased rework.
Other sealant insulating and containment caps have been used such as a single piece cap with an internal threading portion to engage the exposed threads of the threaded portion of the threaded shaft of the metallic bolt assembly which extends beyond the nut of the end portion of the metallic bolt assembly. The single piece cap has limited ability to accommodate properly engaging the threaded bolt shaft and the cap being able to extend to the surface in order to enclose the end portion of the metallic bolt assembly. With the threads of the cap needing to engage one up to and including three threads of the threaded bolt shaft positioned beyond the nut to be properly engage, the distance from the engaged threads of the bolt shaft to the surface varies based on how far, for example, the threaded shaft of the metallic bolt assembly extends from the surface. This distance can also vary based on the size of the nut and/or number of washers positioned on the threaded shaft of the bolt. Thus, with a fixed length of sealant cap, many variations in lengths of these sealant caps would be needed in assembling a complex structure such as an aircraft which would present varying lengths of end portions of the metallic bolt assemblies extending from the surface from which the end portions originate. These variations in lengths of the sealant caps would be needed to enclose and electrically isolate the end portions of the metallic bolt assemblies from sensitive areas within the aircraft.
There is a need for a cap that is not dependent on liquid sealant which drives high installation costs with the high standards placed on fairing for these installations. There is also a need for a sealant cap that can accommodate varying distances from the engagement of the threads of the shaft of the metallic bolt assembly to the surface from which the end portion of the metallic bolt assembly extends. Accommodating these varying distances are needed to properly electrically isolate the end portion of the metallic bolt assemblies but at the same time not driving up cost of installation with needing a large number of different lengths of caps on hand.